Thermoplastic heat exchangers have been made for some time. Efficient plate type units (panels) used in nylon heat exchangers are produced by a twin sheet thermoforming process with internal gas assist, which gives an essentially flat plate consisting of a number of tubes joined by ligatures formed from the sheets of nylon. This process is described in U.S. Pat. No. 5,195,240.
Such plates and the heat exchangers formed from them provide excellent heat transfer efficiency for the space and volume occupied, but can tolerate only relatively low internal pressures, restricting their applicability. Tubing formed by extrusion can tolerate much higher internal pressure. In a high efficiency exchanger a large number of small tubes are required and constraint and support of these tubes is needed. Use of tubing located between two bonded sheets of plastic to achieve this support is described in U.S. Pat. No. 5,469,915. However, this still requires ligatures between the tubes, which reduces heat transfer efficiency. The above-mentioned patents are incorporated herein by reference.
When one tries to bond groups of tubes together without ligatures between the tubes to hold them together, the efficiency of heat transfer from a primary heat transfer fluid inside the tubes to a secondary heat transfer fluid outside the tubes along with the technological process to bond tubes together are factors that can influence the commercial acceptability of the heat exchanger and thus its success or failure at the market place. The arrangement of the tubes in the tube plates can have a significant effect of the flow of coolant outside the tubes.
The present invention provides a heat exchanger comprising thermoplastic tubes having outside and inside surfaces within which tubes flows primary heat transfer fluid and outside of which tubes flows secondary heat transfer fluid, said tubes being adhered together in groups of at least four tubes each, each group having two faces, said groups being arranged in plates of from one to fifty groups, and a multiplicity of said plates being arranged in parallel rows with openings between the rows to permit flow of secondary heat transfer fluid along or across said faces, said faces being configured to minimize laminar flow, to increase turbulent flow of said secondary fluid as it passes over said plates, and to minimize the formation of vortices, with the tubes being arranged either in discontinuous groups within each plate or in a continuous or discontinuous wavy shape with each pair of tubes in each group being at an angle to the adjacent pair of tubes in the same group, measured by connecting lines between the centers of adjacent tubes, between 5 and 30 degrees and with the cumulative angle increasing from tube to tube for at least four tubes, then reversing.
The thermal resistance from the outside of the tubes to the secondary coolant can be less than five times, preferably less than three times, the thermal resistance from the primary coolant to the inside of the tubes.